Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 271023
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
223 AM PST Mon Feb 27 2017

.DISCUSSION...The upper trough that brought several inches of snow to
mountain passes west of the Cascades and up to a foot of snow in the
High Cascades is pushing east and out of the forecast area. Snow
showers are diminishing early this morning, and winter hazard
products have been cancelled a few hours before their original
expiration times.

The cold and showery, northerly flow pattern will not leave
quietly or warm quickly, as a couple more shortwaves embedded in
the flow push south and bring more showers to the area. The next
disturbance will bring increasing showers to Southern Oregon and
Northern California this afternoon (and evening for the East
Side). This system is not as vigorous as Sunday`s and will be
arriving in the afternoon, so most roadways should not see major
winter travel impacts. That said, an inch or so is possible on
lower Interstate 5 passes like Sexton and Canyon Mountain. We have
identified the highest impact area to be Eastern Douglas County
near Toketee Falls along Highway 138 where 3 to 6 inches is expected
over the next 24 hours. We have issued a Winter Weather Advisory for
this area from this afternoon through Tuesday morning. Higher snow
amounts are expected in the Cascades with upslope westerly flow, but
nothing uncommon for that area, and therefore we have not issued any
Advisories for the Cascades.

Yet another disturbance rolls through tonight, and this could cause
more travel impacts in the lower mountain passes west of the
Cascades, due mainly to the fact that road surface temperatures will
be approaching freezing. We`ll let the dayshift evaluate this more
to see if a Winter Weather Advisory is needed, but for now, about an
inch of snow is possible in these areas Monday night.

Conditions dry and warm Tuesday into Thursday before another front
brings the chance for precipitation late Friday.  Snow levels for
this system look to be about 5000 feet. The long-term discussion
from the dayshift follows.

Thursday through Monday...We`ll start off with a broad area of
high pressure across the region. This area of high pressure will
break down as a positively titled trough moves into the Pacific
Northwest. This area of low pressure, and high pressure out over
the Pacific will keep an atmospheric river flowing for the
majority of the extended forecast. This atmospheric river event
isn`t anything extraordinary, but it`s long enough duration that
flooding could be a concern sometime down the line.

The bulk of the moisture in the atmospheric river appears to be
coming with a disturbance, which will be hovering over Hawaii on
Wednesday to Thursday. So this weak atmospheric river event will
have it`s breaks over the days, especially for the inland valleys.

The last thing to mention will be the potential for snow on the
Cascades next weekend.  Mid level flow at 500 mb is westerly with a
55 to 60 knot jet hitting the Cascades.  If this holds, this fits a
typical model of a Cascade snow event. -Smith

&&

.AVIATION...27/06z TAF CYCLE...Showers will continue through the
early morning hours, decreasing some as the morning progresses.
With showers, expect areas of MVFR cigs/vis with local IFR cigs,
especially from the Cascades west through this morning. Also as
showers decrease in coverage local low clouds and fog may develop
in western valleys early this morning, including at KRBG. Areas
of MVFR are expected east of the Cascades with scattered light
snow showers as well tonight into this morning. Snow levels are
expected around 1000 feet tonight through this morning and
locally down to 500 feet elevation. Showers will increase during
the day today, greatest in the later afternoon and evening. A mix
of VFR and MVFR is expected in the valleys, with local IFR in
snow showers through the day. Throughout the period expect partial
obscurations in the mountains to become total, at times, as
rounds of showers move through. -BTL/CC


&&

.MARINE...Updated 200 AM PST Monday 27 February 2017...West swell
and fresh northwest swell will combine to make very steep seas
through this morning and steep seas this afternoon through Tuesday
morning. Weak low pressure over the coastal waters will dissipate
and a ridge will build into the area Tuesday into Wednesday. A weak
front will move onshore Thursday night into Friday and more fronts
will follow into the weekend. Peak seas during that time period are
expected to be around 10 feet at 11 seconds. JRS

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 AM PST early this morning for
     ORZ027-028.
     Winter Weather Advisory from 1 PM this afternoon to 10 AM PST
     Tuesday for ORZ025.

CA...None.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas
from 10 AM this morning      to 10 AM PST Tuesday for PZZ350-356-370-
376.      Hazardous Seas Warning until 10 AM PST this morning for
PZZ350-356-370-376.

$$

NSK/CZS/JRS


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